The Theacea (tea plants) family includes trees or shrubs comprising about 40 genera and 600 species. Camellia sinensis occupies a unique position in the Theacea family, because this particular species of plant is predominantly used as a single raw material source to produce all three basic kinds of tea: green tea, oolong tea, and black tea (collectively referred to herein as the “tea plant”). According to some sources, there is a fourth type of tea, i.e., the so-called “white tea,” which is produced exclusively from the buds or tips of the tea plant.
The three basic forms of tea are determined by the degree of processing, which involves the identical tender young tea leaves. The leaves are plucked, sorted, cleaned, and variously oxidized before steaming or drying. The term “fermentation” is frequently used to describe the processing of tea, but the term “oxidation” is a much more accurate description of the chemical transformations which take place.
Although there are some variations in the processing, it is generally agreed that green tea has the lowest degree of oxidation and that black tea has the highest. Oolong tea is considered to be partially oxidized, and thus occupies the place between green and black tea. With respect to processing, there is very little difference (or no difference at all) between green and white tea.
Green tea is made from fresh leaves that are steamed and wilted, and then immediately dried. Black tea is made from leaves that are wilted and crushed in rollers, then allowed to oxidize for several hours before they are dried. Oolong tea comes from leaves that are only partially oxidized before drying.
Worldwide, tea is the second (after water) most commonly consumed liquid, and is the sixth (after water, soft drinks, coffee, beer, and milk) most commonly consumed liquid in the United States. Tea consumption continues to increase worldwide, especially due to the growing public awareness concerning health benefits of this liquid. There is a growing number of publications suggesting anti-angiogenic, anti-bacterial, anti-cancerogenic, anti-inflammatory, anti-mutagenic, anti-oxidant, anti-septic, and detoxifying properties of teas and their ingredients. The list of tea benefits also includes reduction of the risk of rheumatoid arthritis, lowering cholesterol levels, and anti-diabetic properties. Not all of these benefits have been proven to be statistically significant. Nevertheless, the very broad spectrum of tea benefits reflects the unique composition of the very powerful biologically active substances, which exist in fresh plant leaves and survive conventional tea processing.
In particular, fresh leaves of Camellia sinensis have been reported to contain 22.2% polyphenols, 17.2% protein, 4.3% caffeine, 27.0% crude fiber, 0.5% starch, 3.5% reducing sugars, 6.5% pectins, 2.0% ether extract, and 5.6% ash (Duke, J. A., Handbook of Energy Crops (1983), see www.hort.purdue.edu/newcrop/duke_energy/Camellia_sinensis.html). Per 100 g, the leaf is reported to contain 8.0 g H2O, 24.5 g protein, 2.8 g fat, 58.8 g total carbohydrate, 8.7 g fiber, 5.9 g ash, 327 mg Ca, 313 mg P, 24.3 mg Fe, 50 mg Na, 2700 μg β-carotene equivalent, 0.07 mg thiamine, 0.8 mg riboflavin, 7.6 mg niacin, and 9 mg ascorbic acid. Another report tallies 8.0 g H2O, 28.3 g protein, 4.8 g fat, 53.6 g total carbohydrate, 9.6 g fiber, 5.6 g ash, 245 mg Ca, 415 mg P, 18.9 mg Fe, 60 mg Na, 8400 μg β-carotene equivalent, 0.38 mg thiamine, 1.24 mg riboflavin, 4.6 mg niacin, and 230 mg ascorbic acid. Yet another gives 8.1 g H2O, 24.1 g protein, 3.5 g fat, 59.0 g total carbohydrate, 9.7 g fiber, 5.3 g ash, 320 mg Ca, 185 mg P, 31.6 mg Fe, 8400 μg β-carotene equivalent, 0.07 mg thiamine, 0.79 mg riboflavin, 7.3 mg niacin, and 85 mg ascorbic acid (J. A. Duke and A. A. Atchley, “Proximate Analysis,” In: Christie, B. R. (ed.), The Handbook of Plant Science in Agriculture, CRC Press, Inc., Boca Raton, Fla. (1984)).
Leaves also contain carotene, riboflavin, nicotinic acid, pantothenic acid, and ascorbic acid. Caffeine and tannin are among the more active constituents (Council for Scientific and Industrial Research, 1948-1976). Ascorbic acid, present in the fresh leaf, is destroyed in making black tea. Malic and oxatic acids occur, along with kaempferol, quercitrin, theophylline, theobromine, xanthine, hypoxanthine, adenine, gums, dextrins, and inositol. Chief components of the volatile oil (0.007-0.014% fresh weight of leaves) are hexenal, hexenol, and lower aldehydes, butyraldehyde, isobuteraldehyde, isovaleraldehyde, as well as n-hexyl, benzyl and phenylethyl alcohols, phenols, cresol, hexoic acid, n-octyl alcohol, geraniol, linalool, acetophenone, benzyl alcohol, and citral.
It was found that the fresh tea leaf has an unusually high level of flavanol group of polyphenols (catechins), which may reach up to 30% of leaf dry matter. Catechins include predominantly (−)-epicatechin, (−)-epicatechin gallate, (−)-epigallocatechin and (−)-epigallocatechin gallate. Additionally there are unique to tea 3-galloylquinic acid (theogallin) and unique amino acid theanine (5-N-ethylglutamine) (Duke, J. A., Handbook of Energy Crops (1983), see www.hort.purdue.edu/newcrop/duke_energy/Camellia_sinensis.html).
Tea leaves contain high levels of polyphenol-oxidase and peroxidase. The first enzyme catalyzes the aerobic oxidation of the catechins and this process is initiated when the integrity of the leaf cell structure is disrupted. Phenol-oxidase is responsible for generation of bisflavanols, theaflavins, epitheaflavic acids, and thearubigens, which constitute the largest mass of the extractable matter in black tea. Most of these compounds readily form complexes with caffeine, which has significant level (2-4% of dry matter) in fresh leaves. Peroxidase plays important role in generation of the above complexes with proanthocyanidins. The catechin quinones also initiate the formation of many of the hundreds of volatile compounds found in the black tea aroma fraction. Additionally, the transformation of relatively soluble glycosides to lower solubility aglycones takes place.
All complex cascades of the above processes are initiated by disruption of the leaf cell structure and are intensified with the time of oxidation. As result, the composition of black tea, which is usually processed with intensive rolling or cutting and relatively long time oxidation, is much more different than that of the fresh leaf. Although green tea (and white tea) is processed with minimum oxidation, and its composition more similar to that of fresh leaves, there are non-enzymatic and enzymatically catalyzed changes, which occur extremely rapidly following plucking, and new volatile substances that are produced during the drying stage. Thus, even relatively gentle green tea processing initiates certain departure from original fresh plant composition and can diminish the therapeutic value and other potential benefits of fresh tea plant leaves.
Numerous recent studies clearly demonstrate that therapeutic benefits of tea are decreased in the following sequence: white tea>green tea>oolong tea>black tea. Thus, exploration of fresh tea plants may prevent the degradation of specific activities, which are observed as a result of conventional tea processing. Fresh, tender Camellia leaves contain approximately 80% water. Swelling and dehydration of the cells is prevented by the cells' rigid cell walls. The disruption of the cell wall structure triggers the dehydration of fresh plant tissue followed by the sequence of unwanted physico-chemical and biochemical processes: osmotic shock, decompartmentalization and disruption of enzymes, hydrolysis and oxidation, polymerization of phenols, transformation of glycosides to aglycones, generation of products of Maillard reaction, isomerization, and microbial contamination. Therefore, fresh Camellia contains very broad spectrum of biologically active substances and only part of them became available during conventional extraction processes. Thus, only cell walls, catabolites, and stable metabolites can be extracted with boiled water to obtain tea drink or for extraction with different solvents to obtain limited parts of biologically active components (predominantly polyphenols and flavonoids).
In light of the potential of fresh tea leaves as sources of valuable therapeutic and other potentially beneficial bioactive compositions, exploration of fresh tea plants is needed to determine how to maximize their therapeutic and other potentially beneficial bioactive properties.